During the standardization process of the Third Generation Partnership Project (3GPP) release 10, also known as, Long Term Evolution Advanced (LTE-A), relay nodes (RN) were given consideration. In the 3GPP TR 36.814 V0.4.1, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Further Advancements for E-UTRA Physical Layer Aspects (Release 9),” February 2009, it is stated that “relaying is considered for LTE-Advanced as a tool to improve, e.g., the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and/or to provide coverage in new areas.” A wide variety of relay nodes may currently be under discussion, including smart repeaters, different types of layer 2 (L2) relay nodes such as decode-and-forward, and layer 3 (L3) relay nodes.
Common to all the relay node types is that a relay node is wirelessly connected to a radio-access network (RAN) through a donor cell (or a donor enhanced NodeB (eNB)). A wireless connection between the relay node and the donor cell is crucial especially for relay nodes operating in higher layers since the capacity of the wireless connection may be a bottleneck to the uplink (UL) and downlink (DL) capacity of all user equipments (UEs), or mobile stations, terminals, users, and so forth, served by the relay node.
As used in this discussion, the term layers refer to the lower layers in the Open System Interconnection (OSI) Reference Model, such as physical layer (i.e., layer 1), data link layer (i.e., layer 2), network layer (i.e., layer 3), and so on.
At the RAN1 #56 meeting, it was agreed that at least “type I” relay nodes are to be a part of LTE-A, where “type I RN shall have its own Physical Cell ID (defined in LTE Release 8) and transmit its own synchronization channels, reference symbols.” See R1-091098, “WF on Relaying Operation for LTE-A,” February 2009. At the RAN1 #56bis meeting, it was proposed that a “type II” relay node may be defined for LTE-A. A key characteristic of the type II RN is that “type II RN should not have a separate cell ID and thus would not create any new cell(s),” (R1-091632). Common to the different types of relay nodes is the wireless backhaul link between the relay nodes and the donor cell/donor eNB.
For inband relaying, the eNB-to-relay node link operates in the same frequency spectrum as the relay node-to-UE link. In order to avoid interference between transmissions occurring on the eNB-to-relay node link and the relay node-to-UE link, time-division multiplexing (TDM) has been proposed to multiplex the two links. That is, the relay node does not transmit to UEs when it is supposed to receive transmissions from the donor eNB, and vice versa. Transmissions between the donor eNB and the relay node may occur during backhaul subframes, which are configured as multi-media broadcast over a single frequency network (MBSFN) subframes between the relay node and its UEs.
It is expected that multiple relay nodes may be planted in a coverage area of the same donor eNB to cover its cell edge. In this scenario, multiple relay nodes are wirelessly connected to the same donor eNB. It is not clear how the available resources should be shared between the multiple nodes.